Need to replace my passenger side mirror on my 2014 F Sport ..

just wondering If I can pick one up at a local Lexus.

When I look online at there parts department website it doesn't make much sense to me and I could really figure out of they sold the whole assembly or if I had to buy individual parts and put it all together.

 

Yes they sell the mirror as one complete assembly...price will depend on the color and options (Memory Seats, Blind Spot monitoring, etc.)
They sell the individual pieces as not very often the entire mirror gets damaged.

What is wrong with your mirror? If you need just one part it will be a lot cheaper just to buy it alone.

 

Mirror got slammed into..back housing is cracked, so is the glass, turn signals are good so im hoping that maybe I can just replace the back over as well as the glass. Only thing I couldn't test was the heat & blind spot warning. The cables running behind the mirror itself were still attached and looked undamaged. I saw lex sells the back cover as well as the glass hoping to get down to my local one next week to see if I can purchase just those. we

 

You can get just the cover and glass.
Likely with the damage to the glass is why the heated element and BSM icon aren't working.

 

You will need the whole assembly. Buying just the cover and the mirror will not cut it. You can try to find a mirror assembly from a salvage yard if you're looking for considerable savings. Keep in mind, there is labor charged to disassemble the inner components as you may need to have the outer housing refinished by a body shop.

www.car-part.com is a good place to start for salvaged/LKQ parts. I worked in the collision repair industry for many years in a previous life and have seen this type of damage numerous times.

 

Could I inquire as to how you came to the above conclusion?
The OP stated the mirror still functions except he cannot confirm the heated element or BSM still function...but considering the state of the glass, it's not surprising.
The base, turn signal, and black housing appear to be undamaged...of course you really won't know until the back cover is removed, but it looks very promising that they are fine.

 

Sure. the motor assembly is attached to the backside of the mirror assembly. The BSM and the wiring is clipped into the mirror, however If any of the clips or tabs are broken on the mirror or the mirror assembly, the whole thing is useless. It's usually cheaper to replace the whole assembly than try to replace with a used/salvaged part because the cost sometimes exceeds the actual cost of the part new. Labor time needs to be factored in to be cost effective.

They typically break with damage like this. I've replaced these mirrors with this same damage on countless cars in my 12 year collision repair career.